The Micro-Accelerator Platform
- Author(s): McNeur, Joshua Clarke
- Advisor(s): Rosenzweig, James B
- et al.
Multiple applications in attosecond science, standoff nuclear detection, oil-well logging, and medicine require the use of compact high-gradient accelerators. The microstructure-based field of Dielectric Laser Accelerators (DLA's) lever- ages high-power optical lasers and well-established nanofabrication techniques to accelerate electrons with GV/m electromagnetic fields over mm-scale distances, thus filling providing compact high-gradient acceleration. The Micro-Accelerator Platform (MAP) is a micron-scale slab-symmetric resonant-cavity DLA that ac- celerates electrons with a potential acceleration gradient approaching 1 GeV/m. In principle, electrons are synchronously accelerated as they traverse the stand- ing wave resonance in the MAP's vacuum cavity, excited by a side-coupled Ti:Sapphire laser and confined by Distributed Bragg Reflectors above and be- low the vacuum cavity. Extensive analysis, simulations, and a proof-of-principle experiment show that the MAP is a viable candidate for compact high-gradient acceleration.
A simplified model of the MAP is used to develop analytic expressions of the resonant fields and associated forces in the vacuum cavity of the MAP. These resonant fields are shown to be capable of accelerating electrons with GeV/m acceleration gradients with no transverse defocusing.
To examine the dependence of the quality and frequency of the MAP's reso- nance on it's geometry and component materials, simulations in the frequency- domain EM solver HFSS and the time-domain EM solver and PIC code VORPAL are utilized. After a set of design parameters and materials that are practical to fabricate has been detailed, the quality of the MAP's resonance, spectral char- acteristics of the MAP, error tolerances of the design, ability of the resonance to accelerate electrons, and transverse dynamics of electrons traversing the MAP are presented via simulation results.
Optical lithography and sputtering deposition techniques are used to fabricate the final design of the MAP. After characterization of the fabricated sample is described, the testing of the MAP at the Next Linear Collider Test Accelerator is discussed. A 60 MeV electron beam traverses the MAP as it is illuminated by a Ti:Sapphire laser. The energy spectra of the beam after having passed through the illuminated MAP is then compared to the energy spectra of the beam after having passed through the MAP without laser illumination in order to deduce whether acceleration has occurred. The strength of acceleration versus the relative timing of the laser and electron beam is examined. It is deduced that for a subset of the data collected, the MAP accelerated electrons with a 50.6 MeV/m accelerating gradient. The implications of this finding and potential ways to increase the accelerating gradient are discussed.